Thanks guys! Will do something in the next days/weeks. Until then, try to figure out how it works. Just one additional note: The composite video signal is connected to all three displays without any further electronics. And as mentioned, Audio is connected to audio - that's where the AHX should be, right in your ears!

Nice :) I've a couple of theories on how it works having played with a fair few scopes and TV pattern generators in the past... I wonder if seeing all 3 screens at the same time would give anything away, or turning up the brightness a touch on the TV?

I worked a lot into video editing when this kind of analog oscilloscope was always plugged on the video outputs in video output factories. They're used to check the video levels for luma. Each horizontal blank signal (=line) drives the oscilloscope which draws the luminosity of the line (so if everything's black and one line is 25% gray, wherever it is on TV, on the waveform monitor you get one big flashy line on the bottom and a light line at 25% luma). You can Google Images for "video waveform luma" to find what I mean. Now for cost reasons such analog oscilloscopes are not used anymore, and a lot of editing software include a soft waveform monitor directly in the UI.

At the time I edited some Amiga/ST demos and I already noticed that objects containing raster colors (for instance, scrolltexts) appeared on the waveform monitor, perfectly visible, with different movements on the scope than on the video screen because the up/down movements where driven by the rasters' colors luminosity. That was fun to watch indeed, like another demo in the demo.

So my thoery is that they actually used this plain trick for the first part, the only thing is that it seems they have used slightly different settings to zoom into the waveform graph so that the "borders" of the graph are hidden in the scope borders.

For the second part (the dual screen part), my guess is that they used another setting to further zoom into the oscilloscope graph so that whites and blacks don't show up on the scope, and that they used hidden lines of the video signal to display greyscales that don't show on the TV (overscan) but are still decoded by the scope. Another theory is that they might have used very dark greys in the background to make the scope animation, in any case the scope rendering is very blurry, meaning they had to use only a subset of the scanlines or the luma scale (or both). Also don't forget that analog video use a luma scale that is larger than digital video with underblacks and overwhites.

I don't think the scopes are using the chroma part of the signal since the vertical bars that appears on the edge of some objects is a typical waveform filtering issue.

the original is played back through Paula, so 4x 8bit pcm. I don't know what equivalent mixing frequency would make it sound like Paula... Anyway hvl2wav mixes it down to two stereo 16bit channels. As for the fade out, it is not encoded in the ahx file, it just loops forever. Hvl2wav stops after 10 minutes on looping songs, or you can specify a length. If you want it to fade out, any sound editor can do that easily afterwards.

Heh, I tried that old http://www.the-leaders-of-the-eighties.de/static/download/WinAHX_1_0_Win9xNT.zip and it played forever (looping). I also noticed the instrument notes said the song was unfinished. Hmm!

this is truly the best demo i've ever seen <3
i mean, commodore 64 music made with a tracker developed for the amiga 500 assisted by oscilloscope-drawn graphics, all on a ps2. Dexter, you're the best <3